A known disk such as a WRITE ONCE optical disk is accommodated in a predetermined cartridge in order to protect an information signal from write error and read error caused by smudges due to dust upon non-use when it is not loaded onto a recording and/or reproducing apparatus or due to damage caused when it contacts with a foreign object. This kind of cartridge is disclosed in Japanese Published Patent Gazette No. 61-3015, in which opening portions are formed through upper and lower halves of the disk cartridge in order to expose one portion of a signal recorded portion of the disk accommodated in the disk cartridge and a chucking portion provided at the center of the rotation thereof. Also, in order to prevent at least the signal recorded portion of the disc from contacting with the inner wall of the disk cartridge, disk supporting ribs are protrusively formed within the cartridge. These ribs support the disk at its portion where no signal is recorded.
Of the thus arranged conventional disk cartridges, particularly the disk cartridge where the disk is supported by the integrally formed ribs, the cartridge nevertheless cannot protect the disk from being physically shocked. Thus, if the disk cartridge is subjected to physical shock during its transportation or the like, the disk will be damaged. If a flexible shock absorbing member such as a rubber plate is provided on the inner surface of the cartridge and this shock absorbing member supports the disk, the disk can be protected from the damage caused by the shock. When the weight of the disk is applied to the shock absorbing member, however, the shock absorbing member is bent so that the disk sticks to the shock adsorbing member. Thus, when the disk cartridge is loaded on and rotated by the recording and/or reproducing apparatus, there is then a risk that the disk cannot begin to rotate smoothly. Particularly when the shock absorbing member is made of silicone rubber with sufficient flexibility in order to enhance the shock absorbing effect, the disk sticks to the shock absorbing member noticeably.